As it stands that is not a question

No.I think I heard something about reducing 72 into its lowest prime numbers~ and then list the numbers less than 72 that do not have 2 or 3 as factors? But wouldn't that take a long time?

ProbablyIs there another efficient strategy?

If N is this largest common factor, then for every K which has no factor in common with 72

hcf(NK,72)=N

RonL